The people of Syria are losing hope in the fifth year of a civil war that has brought levels of death and destruction that are so extreme they should shock the world's collective conscience, the United Nations chief said in a report on Syria.

The war has killed more than 220,000 people and left a third of the population homeless. Of the country's roughly 23 million people, some 12.2 million are in need of humanitarian aid, including 5 million children, Secretary-General Ban Ki-moon said in his monthly report published on Wednesday.

"The level of carnage and devastation throughout the Syrian Arab Republic should shock the collective conscience of the world," said Ban's report, which covers the month of April and was largely prepared by outgoing U.N. humanitarian chief Valerie Amos.

"The Syrian people are losing hope," he said. "They cannot afford to wait. A political solution must be found.

"The conflict will end with a political settlement, not with a military solution," Ban added. "The sooner that that is recognized by all those engaged in the conflict, the better it will be for the Syrian people and the more lives will be saved."

Ongoing horror

U.N.-mediated peace talks have resumed in Geneva, but diplomats say no breakthroughs have emerged.

Last month, Amos urged the Security Council to impose an arms embargo and sanctions on Syria for violations of humanitarian law.

Ban accused Syrian government forces of using barrel bombs, which he said indiscriminately harm and kill civilians. He also accused Islamic State militants, who have taken over large swaths of Syria and Iraq, of killing and kidnapping civilians and destroying and damaging Syrian cultural heritage sites.

"Parties to the conflict continue to behave with impunity and total disregard for the basic tenets of humanity and international humanitarian law," Ban's report said.

"It is difficult to believe that those who drop barrel bombs or launch mortar rounds and artillery shells do not realize the immense harm and suffering that their actions are causing to civilians," Ban said.

Syrian President Bashar al-Assad has denied that his forces use barrel bombs, though Western officials and rights groups say the denial is not credible.

Ban reported that humanitarian aid access to civilians remained problematic, partly due to the fighting but also because of obstruction by the parties to the conflict, especially the government. He also said the number of attacks on medical facilities was alarmingly high.